Many electronic display devices, such as monitors, televisions, and phones, are 8-bit depth displays that are capable of displaying combinations of 256 different intensities of each of red, green, and blue (RGB) pixel data. Although these different combinations result in a color palette of more than 16.7 million available colors, the human eye is still able to detect color bands and other transition areas between different colors. These color banding effects can be prevented by increasing the color bit depth to 10 bits which is capable of supporting 1024 different intensities of each of red, green, and blue pixel data. However, since many display device devices only support an 8-bit depth, a 10-bit RGB input signal must be converted to an 8-bit signal to be displayed on a display device.
Many different dither methods, such as ordered dither, random dither, error diffusion, and so on, have been used to convert a 10-bit RGB input signal to 8-bit RGB data to reduce banding effects in the 8-bit RGB output. However, these dither methods have been applied at the display end, only after image data encoded at 10 bits has been received and decoded at 10 bits. These dither methods have not been applied to dithering 10-bit YCbCr to 8-bit YCbCr data before the 8-bit data is encoded and transmitted to a receiver for display on an 8-bit RGB display device.
One of the reasons that these dither methods have not been applied to dithering 10-bit YCbCr data before transmission is that many of the international standards that define YCbCr to RGB conversion cause loss of quantization levels in the output, even in the input and the output signals have the same bit depth. This may occur because the conversion calculation may map multiple input quantization levels into a same output level. The loss of these quantization levels during conversion from YCbCr to RGB negates the effects of applying a dither when converting a 10-bit signal to an 8-bit signal. As a result, the output images may contain banding artifacts.
There is a need to generate display images that do not contain banding artifacts when applying a dither during a bit reduction process as part of a conversion from YCbCr to RGB color space.